This application claims the priority benefit of Taiwan application Ser. No. 88101118, filed Jan. 26, 1999, the full disclosure of which is incorporated herein by reference.
1. Field of the Invention
The invention relates to a direct data access device, and in particular to a direct input/output port access device which can control data accesses directly between an input port and an output port.
2. Description of the Related Art
In general, data accesses to input and output ports in a computer system or a microcomputer control system are controlled by a microprocessor or by a direct memory access (DMA) controller only for individual read and write operations. Under some circumstances, a great amount of data is just required to be transmitted from one output port to another input port. In this case, it is very uneconomical to implement the above-stated operation with a resource-expensive CPU or a DMA controller.
For example, a DVD player having a DVD-ROM built therein is a typical microcomputer control system. A microprocessor included in the DVD player is mostly used to control data accesses in addition to control to internal devices""s operations thereof In the DVD player, the microprocessor controls the DVD-ROM by using an input/output port and can read DVD data out through the input/output port. Except for a minor part of the read DVD data which is processed by the microprocessor and reserved, the major part of the read DVD data remains unchanged and is transmitted to a DVD decoder through an output port. On the other hand, a DMA controller can also be used to perform data accesses to the input and output ports. That is, DVD data are transmitted from the DVD-ROM to the microprocessor""s memory, and then to the DVD decoder. To achieve the above-stated data transmission, the used microprocessor must have a high-performance function, or an additional DMA in coordination with a great amount of memory required. However, it is not a best design for consumer products.
In view of the above, an object of the invention is to provide a direct input/output port access device which can control data accesses directly between an input port and an output port. The direct input/output port access device of the invention includes a local data bus, an input/output port read/write controller and a data bus transceiver. The local data bus electrically connects the input port and the output port. The input/output port read/write controller is electrically connected to the output port and the input port through an output port control/status line and an input port control/status line, respectively for controlling data accesses directly between the output port and the input port through the local data bus. The data bus transceiver is electrically connected to and controlled by the input/output port read/write controller through a data bus transceiver control line for separating the local data bus from a system data bus when data accesses between the input port and the output port is in progress. Therefore, data accesses between the input port and the output port are directly controlled by the input/output port read/write controller with the local data bus electrically separated from the system data bus.
Furthermore, in the direct input/output port access device, the local data bus is used for data transmission through a system data bus or for data accesses directly between the input port and the output port. In a general operating mode, the local data bus is electrically connected to the system data bus, and therefore, the input port and the output port electrically connected thereto can receive/transmit data from/to a system""s any device with the control of a microprocessor. However, in an operating mode for data accesses directly between the input port and the output port, the local data bus is electrically separated from the system data bus, and is used only for data accesses directly between the input port and the output port with the control of the input/output port read/write controller. At this time, the system data bus is still reserved for the microprocessor to implement other operations. In other words, the direct input/output port access device not only increases the data transmission rate directly between the input port and the output port one time, but also reduces the entire load of the system including the microprocessor. Accordingly, the direct input/output port access device of the invention is suitable for a great amount of data accesses required directly between the input port and the output port in a microprocessor control system or a general computer system.